What is homocysteine?

Homocysteine is an amino acid. Amino acids are the building blocks of proteins. It is not possible to get homocysteine from the diet. It must be made from methionine, another amino acid that is found in meat, fish, and dairy products. Vitamins B6 (pyridoxine), B12 and folic acid are needed to make this reaction occur.

Foods containing methionine are transformed into homocysteine in the bloodstream. Homocysteine is converted in the body to cysteine, with vitamin B6 facilitating this reaction. Homocysteine can also be recycled back into methionine using vitamin B12-related enzymes.

Cysteine is an important protein in the body that has many roles. It is involved in the way proteins within cells are folded, maintain their shape, and link to each other. Cysteine is a source of sulfide and is part of the metabolism of different metals in the body including iron, zinc and copper. Cysteine also acts as an anti-oxidant.

If homocysteine cannot be converted into cysteine or returned to the methionine form, levels of homocysteine in the body increase. Elevated homocysteine levels have been associated with heart attack, stroke, blood clot formation, and perhaps the development of Alzheimer's disease.